1. Field of the Invention
The present invention relates to a tube joint for a fluid. In particular, the present invention relates to a tube joint having a detachable mechanism comprising a socket and a plug.
2. Description of the Related Art
A general tube joint for a liquid having a detachable mechanism comprises check valves for both of a socket and a plug. Therefore, no liquid leaks when the plug is disengaged from the socket. For example, FIG. 14 shows a tube joint 500 comprising a socket 502 and a plug 552.
In the following description, as for each of the socket and the plug, the side on which the connection is made is referred to as xe2x80x9cfrontward directionxe2x80x9d or xe2x80x9cfront endxe2x80x9d, and the opposite side on which the socket or the plug is connected to another tube passage (or a hose) is referred to as xe2x80x9crearward directionxe2x80x9d or xe2x80x9crear endxe2x80x9d.
The socket 502 comprises, for example, a cylindrical socket body 504 which has a rear end opening 514 and a front end opening 528, a valve element 506 which has a tapered surface 506b, a pedestal 512 which has a plurality of through-holes, a cylindrical sleeve 520 which is disposed on the outer circumference of the socket body 504 on the front end side and which is fastened by a retaining ring 516 while being urged frontward by a coil spring 522, a plurality of steel balls 526 which are inserted into a plurality of holes each having a gradually reducing diameter near the front end of the socket body 504 and which are pressed by the inner circumferential surface of the sleeve 520, and an O-ring 524 which is disposed on the inner circumferential surface of the front end opening 528.
An annular seal member 510 is disposed on the tapered surface 506b of the valve element 506. One end of the coil spring 508 contacts the pedestal 512. The valve element 506 is urged frontward by the coil spring 508. The seal member 510 and the end surface of an annular projection 504a formed on the inner circumference of the socket body 504 contact each other to thereby function as a check valve which prevents the fluid from leaking frontward. Especially, even when the fluid pressure in the rear end opening 514 is high, the valve element 506 is pressed frontward by the fluid pressure. The liquid tightness (or air tightness) is kept because the tapered surface 506b is tightly inserted by force into the annular projection 504a. 
A forward end surface 506a, which is disposed at the front end of the tapered surface 506b, abuts against the plug 552.
The plug 552 comprises a plug body 554, a valve element 556 which has a tapered surface 556b, and a pedestal 562 which has a plurality of through-holes.
The plug body 554 includes a rear end opening 564, an outer circumferential surface 554b which is disposed on the front end and which is inserted into the socket 502, and an annular groove 554a which functions as a disengagement stopper when the plug body 554 is joined to the socket 502.
An annular seal member 560 is disposed on the tapered surface 556b of the valve element 556. The valve element 556 is urged frontward by a coil spring 558 which has one end fixed to the pedestal 562. The seal member 560 contacts an annular projection 554c which protrudes in the inner circumferential direction at the forward end of the plug body 554 to thereby function as a check valve to prevent the fluid from leaking frontward. The liquid-tight function (or the air-tight function) is the same as the liquid-tight function (or the air-tight function) of the socket 502.
A flat forward end surface 556a at the forward end of the tapered surface 556b abuts against the socket 502.
When the socket 502 and the plug 552 are connected to one another, the force is applied to the rear of the sleeve 520 to move the sleeve 520. The pressing force applied to the steel balls 526 is released. Therefore, the outer circumferential surface 554b at the front end of the plug body 554 can be inserted into the front end opening 528 of the socket 502, while pushing the steel balls 526 out of the socket 502.
The respective forward end surfaces 506a, 556a of the valve elements 506, 556 of the socket 502 and the plug 552 abut each other. When the plug 552 is inserted deeply, the valve elements 506, 556 are moved relatively rearward with respect to the socket body 504 and the plug body 554 while compressing the coil springs 508, 558. Then, the both seal members 510, 560 are separated from the annular projections 504a, 554c to form a connecting flow passage 530 (see FIG. 15). Therefore, the rear end opening 514 of the socket 502 and the rear end opening 564 of the plug 552 are communicated with each other via the through-holes of the pedestals 512, 562 and the connecting flow passage 530. The front end outer circumferential surface 554b of the plug body 554 and the O-ring 524 tightly contact each other to thereby serve as the sealing. Consequently, no fluid leaks externally.
When the plug 552 is sufficiently inserted into the socket 502 and the force applied to the sleeve 520 is released, the sleeve 520 is urged by the elastic restoration of the coil spring 522 and is restored to the original position.
The steel balls 526 are pressed again by the sleeve 520 toward the central axis of the socket body 504. As a result, the steel balls 526 are engaged with the annular groove 554a of the plug body 554.
Owing to the engagement with the steel balls 526, the plug 552 is not disengaged from the socket 502. The socket 502 and the plug 552 are tightly coupled to one another.
In the tube joint 500, each of the socket 502 and the plug 552 uses the check valve mechanism using the tapered surface 506b, 556b of the valve element 506, 556. When the socket 502 is connected to the plug 552, each of the valve elements 506, 556 is moved toward the rear end opening 514, 564. Depending upon the amount of movement, the space of the connecting flow passage 530 is generated at the portion of the tapered surface 506b, 556b. 
During the connection and the disengagement, a gap 532 is generated between the front end surface 554d of the plug body 554 and the end surface 504b which abuts against the front end surface 554d. The gap 532 is generated due to the discrepancy between the timing at which the O-ring 524 and the outer circumferential surface 554b contact each other to form the seal structure and the timing at which the O-ring 524 slides on the outer circumferential surface 554b to allow the front end surface 554d and the end surface 504b to abut (or separate).
When the socket 502 is disengaged from the plug 552 with the connecting flow passage 530 being filled with the fluid, the fluid is extruded by the respective tapered surfaces 506b, 556b. Further, the fluid is drawn by the gap 532 and leaks externally.
An object of the present invention is to provide a tube joint which prevents fluid from leaking in the tube joint when a socket and a plug are connected to and disengaged from each other.
Another object of the present invention is to provide a tube joint in which axial centers coincide with each other to effect correct connection when a socket and a plug are connected to one another.
According to the present invention, there is disposed a tube joint for a fluid, comprising a socket and a plug which is connected to and disengaged from the socket; wherein the socket or the plug comprises an outflow-preventive valve for closing a passage for the fluid with a cylindrical valve body which is coaxial with the socket or the plug and a valve element which is disposed in the valve body when the socket and the plug are disengaged from each other; and a first seal for sealing the socket and the plug before the valve body and the valve element are relatively moved when the socket and the plug are connected to one another.
Therefore, when the socket and the plug are coupled to or disengaged from each other, the fluid in the tube joint does not leak. Further, the interior of the tube joint is not contaminated by the external air.
The first seal may be disposed on an inner circumferential annular groove of the valve body of the socket.
The first seal may be disposed on an outer circumferential annular groove of the valve body of the plug.
A tapered surface, which is diametrally enlarged frontward, may be disposed at a front end of the valve body of the socket.
Accordingly, the axial center of the socket coincides with the axial center of the plug by the guiding action of the tapered surface for the correct connection.
The first seal may be disposed on at least one of end surfaces at which the socket and the plug abut with each other.
The valve bodies of the plug and the socket may tightly contact each other and the valve elements of the plug and the socket may tightly contact each other when the outflow-preventive valve closes the passage for the fluid when the socket and the plug are disengaged from each other. It is possible to prevent the fluid from externally leaking.
The socket or the plug may include a detachable mechanism for the socket and the plug which are coupled to and disengaged from each other.
The valve element may have a second seal on an outer circumference of a front end columnar section thereof. The second seal may be interposed by an inner circumferential surface of the valve body and an outer circumferential surface of the valve element when the socket and the plug are not coupled to one another. Accordingly, it is possible to prevent the outflow of the fluid.
The valve element may have a projection or a recess for adjusting an axial center of the socket or the plug. The projection or the recess is formed on an end surface of the valve element. The end surface thereof is coupled to the socket or the plug.
The tube joint may further comprise a cylindrical groove which is open rearward between an inner circumferential surface and an outer circumferential surface of the valve body. One end of an elastic member for urging the valve body in an axial direction of the socket or the plug may be inserted into the cylindrical groove.
Each of the socket and the plug may have, at each rear end thereof, a rear end joint section connected to another tube joint. A first connecting section for connecting a main body of the socket to the rear end joint section may have the same shape as that of a second connecting section for connecting a main body of the plug to the rear end joint section.
Each of the socket and the plug may have, at each rear end thereof, a rear end joint section connected to another tube joint. The rear end joint section may have a hexagonal cross section which is perpendicular to an axial center.
The above and other objects, features, and advantages of the present invention will become more apparent from the following description when taken in conjunction with the accompanying drawings in which a preferred embodiment of the present invention is shown by way of illustrative example.